1. Field of the Invention
The present invention relates to gas turbine engines and, more particularly, to combustion chambers for use therein.
2. Description of the Prior Art
Gas turbine engine efficiency is a function of various parameters, among them the temperature achievable within combustion chambers, as well as the amount of air which must be diverted to cool various components of the engine. Contemporaneously, the structural integrity of an engine is improved if structural loads are carried by engine components which are not also subjected to high temperatures and attendant thermal stresses.
In an attempt to raise achievable temperatures within combustion chambers, various materials and alloys have been proposed and used in the construction of the chambers. Among those materials which exhibit particularly beneficial resistance to thermal effects are so-called superalloys, oxide dispersion strengthened materials, and various ceramics. This invention may employ these and other appropriate materials in the construction of the improved combustion chamber being disclosed.
The effective application of such high temperature materials as those discussed, in addition to enabling higher temperatures to be reached, also allow a reduction in the amount of cooling fluid required to be directed to the combustion chamber during operation. This reduction enables the engine to operate with increased efficiency.
Structural failures in gas turbine engines in the past have sometimes resulted from the subjection of structural load-bearing portions of the engine to thermal stresses associated with high temperatures of combustion. The formation of a combustion chamber in a way that requires the chamber liner (which is directly exposed to the heat of combustion) to carry structural loads associated with the combustion chamber has sometimes resulted in such failures.
For some time now, in order to achieve the cooling required while effectively withstanding the structural and thermal stresses to which the components of a combustion chamber are subjected, it has been known to provide spaced walls formed at the inner surface of the combustion chamber and attached end over end in louver fashion to form the combustion chamber, and further to provide a plurality of open-ended longitudinal passageways. By reason of the louver construction, the upstream end accepts cooling air from the surrounding space and discharges it from the passageways at the downstream end into the combustion chamber. Succeeding louver sections pick up and discharge the cooling air in a like manner.
U.S. Pat. No. 4,302,941 discloses such a construction in which a hot liner wall is segmented in both the axial and circumferential direction. The axial segments are sufficiently spaced whereby film cooling provides adequate cooling between axial segments and the space between segments in the circumferential direction permit circumferential growth. The circumferential growth negates the possibility of radial growth and minimizes detrimental thermal stress and leaves the cooling flow passages relatively undisturbed. According to that patent, each segment may be secured relative to a cool wall by a nut and bolt arrangement designed to achieve minimum stresses.
An improved construction is disclosed in U.S. Pat. No. 4,512,159 according to which the liner segments are attached by a spring clip adapted to fit onto an integral post machined on the segment so as to preload the panel in a radial direction. Because this is virtually the only load on the spring clip notwithstanding the high temperature environment, such a retention system is said to be highly durable, improving the maintainability of the combustor liner. Since the clips are removable without damage to the post, the removal of panels is facilitated which are also said to enhance the maintainability of the combustor. Unfortunately, this system exhibits serious drawbacks including the cost of machining large numbers of the posts on the liner segments as well as the large number of resulting irregular-shaped protuberances thereby created on an outer surface of the outer shell.